From 8a730bab6b8b3e661111c696eecfb2e65cd16d59 Mon Sep 17 00:00:00 2001
From: dotCooCoo <RobertLeeLW@gmail.com>
Date: Thu, 5 Nov 2026 20:03:54 -0800
Subject: [PATCH] Reject invalid New Art Basic parameters

---
 crates/engine/src/cmd/newart.rs   |  4 ++--
 crates/engine/src/tests/newart.rs | 14 ++++++++++++++
 docs/mcp.md                       |  1 +
 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/crates/engine/src/cmd/newart.rs b/crates/engine/src/cmd/newart.rs
index 9401402c5..34db64081 100644
--- a/crates/engine/src/cmd/newart.rs
+++ b/crates/engine/src/cmd/newart.rs
@@ -16,7 +16,7 @@ use vectorcraft_doc::{Appearance, AppearanceItem, FillLayer, GraphicStyle, Node,
 use vectorcraft_tools::PaintDefaults;
 
 use super::gradient::unplaced;
-use super::{CommandSpec, Result, Session, always, cmd};
+use super::{CommandSpec, Result, Session, always, cmd, switch_or};
 
 pub fn specs() -> Vec<CommandSpec> {
     vec![
@@ -216,7 +216,7 @@ impl Session {
 }
 
 fn set_basic(s: &mut Session, p: &Value) -> Result<Value> {
-    let on = p.get("on").and_then(Value::as_bool).unwrap_or(!s.prefs.new_art_basic);
+    let on = switch_or(p, "on", !s.prefs.new_art_basic, "appearance.setNewArtBasic")?;
     s.prefs.new_art_basic = on;
     Ok(json!({ "on": on }))
 }
diff --git a/crates/engine/src/tests/newart.rs b/crates/engine/src/tests/newart.rs
index 6bc5eb48b..0f41a5b9d 100644
--- a/crates/engine/src/tests/newart.rs
+++ b/crates/engine/src/tests/newart.rs
@@ -29,6 +29,20 @@ fn undo_len(s: &Session) -> usize {
     s.doc().unwrap().history.undo.len()
 }
 
+#[test]
+fn invalid_new_art_basic_parameters_keep_the_preference_unchanged() {
+    let mut s = session();
+    let undo = undo_len(&s);
+    for params in [json!({"on": "false"}), json!({"on": 1})] {
+        assert!(s.execute("appearance.setNewArtBasic", &params).is_err(), "accepted {params}");
+        assert!(s.prefs.new_art_basic, "changed the preference for {params}");
+        assert_eq!(undo_len(&s), undo, "recorded undo for {params}");
+    }
+    // Left out, or null as for every command, it toggles.
+    assert_eq!(s.execute("appearance.setNewArtBasic", &json!(null)).unwrap(), json!({"on": false}));
+    assert_eq!(s.execute("appearance.setNewArtBasic", &json!({"on": null})).unwrap(), json!({"on": true}));
+}
+
 #[test]
 fn stroke_options_set_with_nothing_selected_carry_to_the_next_object() {
     let mut s = session();
diff --git a/docs/mcp.md b/docs/mcp.md
index 87ac5085c..26f38f758 100644
--- a/docs/mcp.md
+++ b/docs/mcp.md
@@ -3721,6 +3721,7 @@ style; `add: true` stacks it) set that template instead of editing art. With the
 Appearance off (`appearance.setNewArtBasic {on: false}`, the preference `newArtBasic`) new art takes the whole
 appearance of the last selected object. `appearance.newArt` reports what the next object gets; `paint.default`
 resets it.
+`appearance.setNewArtBasic` rejects an `on` value that is not a boolean. Omitting `on` toggles the current preference.
 
 ```json
 {"name":"run_command","arguments":{"command":"select.none","params":{}}}